(1) Field of the Invention
The present invention relates to a channel seizure system and a channel seizure method for seizing communication channels.
(2) Description of the Related Art
In the common channel signaling system, a dedicated circuit for transmission of signaling information for a plurality of speech circuits is provided separately from the plurality of speech circuits. The common channel signaling system enables various service functions such as functions of data exchange and remote maintenance of exchanges in addition to the conventional functions of telephone exchange, and these functions are currently realized, for example, in ISDN.
On the other hand, recently the world has entered the age of multimedia network, and demand for high-speed data transfer, video communication, and the like is growing. Therefore, it is expected that networks having a great capacity and a broad bandwidth and providing high-speed communication service are constructed.
In the common channel signaling system, the ITU-T recommendation Q.763 provides a channel seizure method for establishing a communication path which realizes high-speed communication by concurrently seizing a plurality of consecutive communication channels (i.e., a plurality of communication channels having consecutive channel numbers).
FIGS. 11A and 11B are provided for explaining the principle of the channel seizure method. In FIG. 11A, exchanges 100 and 200 are connected through a plurality of communication channels CH1 to CH10 and a signaling line DL, where the communication channels CH1 to CH10 are provided for transmitting user data, and each of the communication channels CH1 to CH10 has a bandwidth of 64 Kbps.
For example, when a bandwidth of 384 Kbps (=64 Kbpsxc3x976) is required for a video conference, first, the exchange 100 sends a call request (for a multirate call using more than one communication channel) to the exchange 200 through the signaling line DL. At this time, the leading channel of the more than one communication channel for the multirate call is arbitrarily selected. In this example, it is assumed that the leading channel is the communication channel CH4. Then, the exchanges 100 and 200 seize six consecutive communication channels beginning from the communication channel CH4 (i.e., communication channels CH4 to CH9) to establish a communication path, as illustrated in FIG. 11B. Thus, the video conference can be held.
As described above, in order to perform communication with a broad bandwidth, a required number of consecutive communication channels are seized according to the type of information to be transmitted and the purpose of the communication.
However, according to the conventional channel seizure method, it is impossible to seize all of the required number of communication channels unless the required number of consecutive idle communication channels exist. That is, conventionally, idle communication channels located at intervals cannot be allocated to a single multirate call. This is because the ITU-T recommendation Q.763 specifies that communication channels for the multirate call are selected from consecutive idle communication channels.
For example, if the channel CH9 is used in another existing call when the above call request for a multirate call using six communication channels beginning from the channel CH4 is sent to the exchange, the exchange cannot seize six communication channels, since all of the consecutive communication channels CH4 to CH9 are not available due to the occupation of the communication channel CH9, and idle communication channels located at intervals, e.g., a set of the idle communication channels CH4 to CH8, and CH10, cannot be allocated to a single multirate call.
Therefore, conventionally, the above call request has to be repeated until the preoccupied channel CH9 becomes available. Thus, call loss is increased.
In spite of the above problem, conventionally, communication channels are seized regardless of usability of idle communication channels remaining after the seizure, and therefore communication channels cannot be used efficiently.
For example, if a channel CH10 is seized in response to a call request after communication channels CH4 to CH9 have been seized, it is still possible to establish a communication path for a further multirate call of a bandwidth corresponding to three communication channels since three consecutive communication channels CH1 to CH3 are still available.
Nevertheless, since conventionally usability of the remaining idle communication channels is not considered when a communication channel is seized for a call, for example, the channel CH1, instead of the above channel CH10, may be seized in response to the above call request after the communication channels CH4 to CH9 have been seized. In this case, the maximum length of the series of consecutive idle communication channels left for a further multirate call is two. Therefore, idle communication channels cannot be used efficiently.
An object of the present invention is to provide a channel seizure system in which channel allocation is optimized so that usability of idle communication channels in multirate calls is enhanced.
Another object of the present invention is to provide a channel seizure method by which channel allocation is optimized/so that usability of idle communication channels in multirate calls is enhanced.
According to the first aspect of the present invention, there is provided a channel seizure system having a source-side exchange and a destination-side exchange. In the channel seizure system, the source-side exchange contains a channel-state-information holding unit which holds information on a plurality of states of a plurality of communication channels, an optimum-channel determining unit which determines at least one optimum communication channel for use in a first call, from among the plurality of communication channels, based on the information on the plurality of states of the communication channels, a channel seizing unit which seizes the at least one optimum communication channel determined by the optimum-channel determining unit, and a source-side signaling control unit which transmits and receives signaling information. The above optimum-channel determining unit determines the at least one optimum communication channel for use in the first call so that a further operation of seizing consecutive communication channels for a second call can be successfully performed with high probability, after the optimum-channel determining unit determines the at least one optimum communication channel for the first call. The destination-side exchange in the channel seizure system contains a destination-side signaling control unit which transmits and receives the signaling information.
According to the second aspect of the present invention, there is provided a channel seizure method for seizing at least one communication channel for use in a first call. The channel seizure method includes the steps of: (a) holding information on a plurality of states of a plurality of communication channels; (b) determining, as the at least one communication channel for use in the first call, at least one optimum communication channel from among the plurality of communication channels, based on the information on the plurality of states of the communication channels; and (c) seizing the at least one optimum communication channel determined in step (b). The operation of step (b) is performed so that a further operation of seizing consecutive communication channels for a second call can be successfully performed with high probability, after the operations of steps (b) and (c) for the first call.
The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiment of the present invention by way of example.